The present invention relates to rigid crosslinked polymers comprising a combination of low levels of a chemical crosslinking agent and high levels of chain entanglement crosslinking. The crosslinked polymers of the present invention can be utilized as proppants, as ball bearings, as lubriglide monolayers, and for drilling mud applications.
The rigidity of polymers can be enhanced by utilizing high levels or concentrations of polyfunctional crosslinking agents. Most crosslinked polymers can be manufactured by suspension or droplet polymerization where a liquid monomer mixture is dispersed or suspended in an immiscible liquid medium. Suspension polymerization produces spherical polymer particles that can be varied in size by a number of mechanical and chemical methodologies. These methodologies for making crosslinked polymers are well known and practiced in the art of suspension polymerization.
All of the crosslinking agents known in the art are chemical crosslinkers. There are many polyfunctional crosslinking agents in use, but the most prominent crosslinking monomer is divinylbenzene. Divinylbenzene is used to make insoluble, rigid polymers from acrylate esters, methacrylate esters, vinyl acetate, styrene, vinylnaphthalene, vinyltoluene, allyl esters, olefins, vinyl chloride, allyl alcohol, acrylonitrile, acrolein, acrylamides, methacrylamides, vinyl fluoride, vinylidene difluoride, etc. Almost any molecule carrying a vinyl group (Cxe2x95x90Cxe2x80x94) can be crosslinked and made rigid by copolymerization with divinylbenzene. Other crosslinking monomers are polyfunctional acrylates, methacrylates, acrylamides, methacylamides and polyunsaturated hydrocarbons.
Another crosslinking methodology known in the art is macroneting. In macroneting, a preformed polymer is swelled in a difunctional reactant and crosslinked with the assistance of a catalyst. An example of macroneting is the crosslinking of polystyrene swelled in a dihalohydrocarbon by the action of a Friedel-Crafts catalyst such as aluminum chloride or ferric chloride.
The beads of this invention differs from the prior art in that the polymeric beads are made rigid and nonelastic by the physical crosslinking of chain entanglement rather than by the chemical crosslinking of polyfunctional monomers.
Accordingly, the object of the present invention is to provide a polymer with enhanced rigidity having high levels of chain entanglement crosslinking.
Another object of the present invention is to provide a polymer with enhanced rigidity having a combination of low levels of chemical crosslinking agents and high levels of chain entanglement crosslinking.
Still another object of the present invention is to provide a rigid, spherical polymer that reduces work energy and performs numerous mechanical advantages.
Yet another object of the present invention is to provide a polymer with enhanced rigidity that can be utilized as a lubricant in drilling mud formations, as proppants in tertiary oil recovery from wells, as ball bearings for wheels constructed from an engineering plastic, and as a lubriglide monolayer for moving heavy equipment.
A further object of the present invention is to provide a method of manufacturing a polymer with enhanced rigidity.
Another further object of the present invention is to provide a method of manufacturing a drilling mud application, a lubricant, a proppant, a ball bearing and a lubriglide monolayer with enhanced rigidity.
The present invention accordingly relates to a polymer with improved rigidity and having high levels of physical crosslinking properties resulting from chain entanglement. The geometry of the polymer can be beads, spheroids, seeds, pellets, granules, and mixtures thereof. In one embodiment, the polymer of the present invention comprises a combination of low levels of a chemical crosslinking agent and high levels of chain entanglement crosslinking. The physical strength of the polymer is a result of both the chain entanglement and the chemical crosslinking agents.
The chemical crosslinking agent of the polymer comprises from about 1.0% to about 50% by weight of the polymer. In one embodiment, the chemical crosslinking agent is divinylbenzene in the amount from about 1.0% to about 50% by weight of the polymer.
In another embodiment, the chemical crosslinking agent of the polymer is selected from a group consisting of trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, trimethylolpropane dimethacrylate, and trimethylolpropane diacrylate.
In a further embodiment of the invention, the chemical crosslinking agent of the polymer can be selected from a group consisting of pentaerythritol tetramethacryalate, pentaerythritol trimethacrylate, pentaerythritol dimethacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate and pentaerythritol diacrylate.
In still a further embodiment, the chemical crosslinking agent can be selected from a group consisting of ethyleneglycol dimethacrylate, ethyleneglycol diacrylate, diethyleneglycol dimethacrylate, diethyleneglycol diacrylate, triethyleneglycol dimethacrylate and triethyleneglycol diacrylate.
In another embodiment of the present invention, the chemical crosslinking agent is a bis(methacrylamide) having the formula: 
R1 and R2 can be H, alkyl group or aryl group
y=1-100
In yet another embodiment, the chemical crosslinking agent is a bis(acrylamide) having the formula: 
R1 and R2 can be H, alkyl group or aryl group y=1-100
In a further embodiment, the chemical crosslinking agent is a polyolefin having the formula:
CH2xe2x95x90CHxe2x80x94(CH2)xxe2x80x94CHxe2x95x90CH2
where x=1 to 100
In still another embodiment, the chemical crosslinking agent is a polyethyleneglycol dimethacrylate having the formula: 
x=2-100
In another embodiment, the chemical crosslinking agent is polyethyleneglycol diacrylate having the formula: 
x=2-100
In one embodiment, the chain entanglement of the polymer is produced by a rapid rate polymerization procedure. The procedure comprises the step of elevating a radical flux by employing large concentrations of an initiator within the range from about 1.0% to about 10% weight of the monomers and elevating the polymerization temperature to a temperature greater than the ten-hour half-life temperature by an increasing temperature ramp.The ten-hour half-life temperature is the temperature when half of the initiator decomposes in ten hours.
In another embodiment, the radical flux is kept constant throughout the period of polymer growth by a temperature ramping rate that matches the decreasing first order rate of decay of radical concentration. In a further embodiment, the radical flux is a continually increasing value by employing both multiple initiators with increasing decomposition temperatures and an increasing temperature ramp.
In a still further embodiment, the temperature ramping rate for polymerization is one degree centigrade (Celsius) every three minutes. Such a temperature ramp for polymerization can be continuous or can be a series of step functions of temperature increases followed by plateaus of varying length so that the temperature ramp has the form of increasing steps.
The initiators can be selected from a group consisting of peroxydicarbonates, diacyl peroxides, peroxyesters, dialkyl peroxides, peroxyketals, ketone peroxides, peroxyacids, azo compounds, photo initiators and mixtures thereof.
The above-mentioned polymers of the present invention can be used as a proppant, as a ball bearing, as a lubriglide monolayer, and for oil and gas drilling applications.
The present invention also provides a method of manufacturing rigid polymers having high levels of crosslinking. In one embodiment, the method comprises the step of generating chain entanglement by rapid rate polymerization. The rapid rate polymerization procedure comprises the step of elevating a radical flux by employing large concentrations of an initiator within the range from about 1.0% to about 10% weight of monomer weight and elevating the polymerization temperature to a temperature greater than the ten-hour half-life temperature of the initiator. The radical flux is also elevated by an increasing temperature ramp. The radical flux can also be kept constant throughout the period of polymer growth by a temperature ramping rate that matches the decreasing first order rate of decay of radical concentration. The radical flux can be a continually increasing value by employing both multiple initiators with increasing decomposition temperatures and an increasing temperature ramp. A preferred temperature ramping rate is one degree centigrade (Celsius) every three minutes. The temperature ramp of the radical flux can also be a series of step functions of temperature increases followed by plateaus of varying lengths so that the temperature ramp has the form of increasing steps. In another embodiment, the method further comprises the step of adding low levels of chemical crosslinking from about 1% to about 50% of the polymer weight and preferably from about 1% to about 10% of the polymer weight.